During rolling of metal strip, if the strip is to achieve a satisfactory degree of flatness, it is necessary to match the roll gap to the profile of the incoming strip in such a way that the relative reduction at all zones across the strip width is constant. If a mis-match occurs, then this will lead to a local variation in reduction which in turn will produce longer or shorter elements in the strip. During rolling, flatness errors may be concealed because the strip is stretched elastically. The flatness of the strip is directly related to the tension distribution across the width of the strip and hence, by detecting this tension distribution during the rolling process, an indication of the flatness quality of the strip being rolled can be obtained.
A mill operator has three adjustments which be can use to bring about improved flatness in strip being rolled. These adjustments are-bending control of the mill rolls, steer control and roll temperature control. At rolling speeds which are common at the present time, it is difficult for an operator to use these various controls manually in order to produce strip material with an acceptable flatness and quality.